Testing integrated circuit using an A/D converter built in a semiconductor chip

ABSTRACT

A testing integrated circuit for a semiconductor chip, having an integrated circuit, includes a selector, provided in the integrated circuit of the semiconductor chip, for selecting one of a first set of signals supplied from external portions of the semiconductor chip and a second set of signals used for measuring voltages at respective predetermined portions in an internal circuit of the semiconductor chip. The first set of signals is converted from analog to digital signals during a normal operation of the semiconductor chip. An analog-to-digital converter provided in the integrated circuit receives an analog signal output from the selector and produces a digital signal. A plurality of output pads disposed in the semiconductor chip transmits the digital signal from the analog-to-digital converter to the external portions. The output pads correspond to a bit quantity of the analog-to-digital converter.

This is a division of application Ser. No. 07/747,333, filed Aug. 20,1991, now U.S. Pat. No. 5,184,162.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a testing integrated circuit formeasuring an output voltage of an analog circuit in an internal circuitof LSI.

2. Description of the Related Art

There are often cases in which a voltage of an internal circuit of LSImust be measured to evaluate the reliability of LSI. For example, thefollowing methods for measuring the voltage of the internal circuit canbe considered at the trial manufacture:

FIG. 1 shows a structural view explaining the voltage of the internalcircuit of an LSI chip by a testing probe. At the time of the trialmanufacture, the surface of the chip is exposed to facilitate theexamination and analysis. A small pad 22 is formed on an LSI chip 21 tomeasure the voltage. The small pad 22 is formed such that a probe cancontact thereto in advance. A probe 23 is brought into contact with thesmall pad 22. A signal is suitably supplied to a pad 24 and an output ofan internal circuit 25 is measured by a voltmeter 26 connected to theprobe 23. By use of the above-mentioned structure, it is possible tomeasure the voltage of the target portion at an early stage immediatelyafter a wafer is manufactured.

However, in the above-mentioned measuring method, it is complicated tobring the probe 23 into contact with the small pad 22, and it takes muchtime to measure the voltage. Moreover, such measurement using the probe23 cannot be performed after assembly such as packaging. Furthermore, ina case where the small pad 22 is not provided in advance, it becomesvery difficult to contact the probe 23 to a wire itself.

At the time of the production of the LSI chip in which the trialmanufacture is finished, there is a case in which the voltage of theinternal circuit is measured and inspected to discriminate between goodproducts and inferior products. This is a method in which a wire of thecircuit to be measured is extended to a bonding pad and voltage ismeasured from the outside of the pad after assembly. Since this methodcan be performed during a general product inspection, required time formeasurement is reduced. It is possible to perform such measurementbefore or after packaging. However, a pad for measurement must beprovided. There is another case, however, in which a pad for measurementcannot be newly increased in view of the chip layout. In such a case,other pads can be used as a pad for measurement. However, in such acase, an extra burden must be imposed on the design.

In the above two examples, of course, a voltmeter for measuring avoltage must be provided.

Moreover, in recent years, a method has been widely used in which anelectron beam is directly incident on the wire on the chip, and a signalis observed by the amount of mobile electrons. This method is excellentin resolution, but improper for voltage (current) measurement.

Summary of the Invention

An object of the present invention is to provide a semiconductor testingintegrated circuit that can accurately measure a voltage of an internalcircuit without taking much time.

The above object can be achieved by providing a semiconductor testingintegrated circuit including a selector provided in an integratedcircuit of a semiconductor chip and selecting either an external signalsupplied from an external portion of the chip or an internal signalgenerated by an internal circuit of the chip, and outputting theselected signal; an A/D converter provided in the integrated circuit,and inputting the signal from the selector; and a plurality of outputpads of the semiconductor chip transmitting an output of the A/Dconverter to the external portion.

According to the present invention, a testing integrated circuit isstructured by use of the A/D converter built in the semiconductor chip.A signal selecting circuit, which selects the external signal of thesemiconductor chip and the internal signal, is connected to the A/Dconverter. At the time of testing, the internal signal is input to theA/D converter, and the voltage value of the internal signal is obtaineddigitally.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a structural view showing a conventional parametric test,which measures a voltage of an internal circuit of an LSI chip by use ofa probe;

FIG. 2 is a circuit diagram showing the structure of a first embodimentof the present invention;

FIG. 3 is a circuit diagram showing the structure of a second embodimentof the present invention;

FIG. 4 is a circuit diagram showing the structure of a third embodimentof the present invention;

FIG. 5 is a circuit diagram showing the structure of a fourth embodimentof the present invention; and

FIG. 6 is a circuit diagram showing the structure of a fifth embodimentof the present invention.

Detailed Description of the Preferred Embodiments

An LSI is often used in which an A/D converter is provided in anintegrated circuit. A signal serving as an input for the A/D converteris generally supplied from an external portion of a chip. However, it israre that the internal signal of the chip is converted from analog todigital (A/D-converted). According to the present invention, a testingintegrated circuit is structured, that A/D-converts the internal signalof the chip. The embodiments of the present invention will be explainedwith reference to the drawings.

FIG. 2 is a circuit diagram showing the structure of the testingintegrated circuit formed in the LSI chip according to the firstembodiment of the present invention.

An amplifier 1 is provided in the LSI chip, and a signal 2 is outputfrom the amplifier 1. The signal 2 is used to measure a voltage of theinternal portion of the chip, and supplied to a selector 3. A signal 5of the external chip is supplied to the selector 3 from an input pad 4.The selector 3 selects either the signal 2 of the internal circuit orthe signal 5 of the external portion of the chip, and supplies theselected signal to an A/D converter 6. In general, the A/D converter 6inputs the signal 5 from the selector 3. In other words, the converter 6normally performs the original circuit operation.

At the time of LSI reliability test, the input of the A/D converter 6 ischanged to receive the signal 2 from the selector 3 to measure thesignal. Then, the A/D converter 6 operates to transmit its output to outpads 7, and the result of the A/D conversion is read from the externalportion of the chip. It is noted that the number of output pads 7 isprovided in accordance with the number of bits of the A/D conversion.The selector 3 may be program-controlled in the internal portion of thechip, or a test mode signal may be supplied thereto from the externalportion of the chip.

FIG. 3 is a circuit diagram of the structure showing the secondembodiment of the present invention. This embodiment shows a case inwhich a plurality of signals 2 whose voltages are measured and aplurality of signals 5 are used. The same reference numerals as in FIG.2 represent the same devices in FIGS. 3 and thus, explanation isomitted. The selector 3 selects either the plurality of signals 2 or theplurality of signals 5, and the selected signals are sent to the A/Dconverter 6. The remaining operations of this embodiment is the same asthat of the embodiment of FIG. 2.

FIG. 4 is a circuit diagram of the structure showing-the thirdembodiment of the present invention. This embodiment shows a case inwhich a microcomputer is mounted on the same chip. The same referencenumerals as in FIG. 2 represent the same devices in FIG. 4, andexplanation is omitted. A necessary signal process is performed such asa process in which measuring value, which was A/D-converted by the A/Dconverter 6, is sent to a microcomputer 9 via an internal data bus 8,and is distributed to each port at a predetermined time series.Thereafter, the signal is output to the external portion from the pads7. By use of the microcomputer 9, the voltage measurement of one portionis sampled many times, and the signals are equalized, so that noise canbe removed. As a result, the voltage of the internal portion of the chipcan be measured with high accuracy.

FIG. 5 is a circuit diagram of the structure showing the fourthembodiment of the present invention. Control signals 10 and 11 arerespectively sent to the selector 3 and the A/D converter 6 from themicrocomputer 9 of FIG. 4. The selector 3 and the converter 6 arerespectively program-controlled by the control signals 10 and 11.

FIG. 6 is a circuit diagram of the structure showing the fifthembodiment of the present invention. The selector 3, the A/D converter6, and a memory 13, which are provided in the chip, are controlled by acontrol signal 12 sent from the microcomputer 9 of FIG. 4. Further, acomparator 14 is provided that compares the output of the memory 13 withthat of the A/D converter 6. The output of the comparator 14 is fetchedfrom the output pad 7.

Therefore, if the A/D converter is controlled by the microcomputer 9 inmeasuring the voltage, this invention can be applied to not only theparametic test of the chip but also self-diagnostic of the internalcircuit after the circuit is shipped as a product. For example, anexpectation value is stored in the memory 13 in advance, and themeasured value of the internal circuit and the expectation value arecompared with each other by the comparator 14. Thus, if the two valuesare different, then an determined.

According to the above-mentioned embodiments, there is no need for themeasuring probe, the operation of which is complicated in measuring thevoltage of the internal circuit on the LSI chip. Therefore, time neededfor measuring is greatly reduced. Furthermore, it is possible to measurethe voltage of the internal circuit by the signal sent from the externalportion even when the chip has been packaged and the surface of the chipis completely covered. Moreover, it is unnecessary to prepare the padfor taking the voltage measurement outside of the chip. Regarding themeasuring method, only the output value of the A/D converter need beread, and there is no need for a new pad, which is used only for thevoltage measurement.

Moreover, according to the present invention, since voltage measuringmeans is provided in the internal portion on the LSI chip, it isunnecessary to specially prepare a measuring device (voltmeter) outsideof the chip. Also, the measured voltage result of the internal circuiton the LSI chip can be obtained digitally. Therefore, if suitable signalprocessing means such as a microcomputer is used, the storage of themeasured value and signal processing can be easily performed. As aresult, various LSI reliability tests can be realized. For example, itis possible to store the measured result in the memory and read out theresult as necessary. Also, the measured result can be sampled manytimes, which is helpful to prevent erroneous measurement from being madedue to noise.

The testing integrated circuit of the present invention is not limitedto a testing integrated circuit of a semiconductor chip. As shown inFIG. 6, the design value and the measured value are compared with eachother in advance, therefore the voltage measurement of the internalcircuit can be used to the original circuit operation.

As mentioned above, according to the present invention, the voltage ofthe internal circuit on the semiconductor chip can be obtained in theform of the digital value by use of the A/D converter built in the chip.Hence there is no need of a measuring device outside of the chip.Moreover, there is no need of a new pad, which is used only for thevoltage measurement. Therefore, a semiconductor testing integratedcircuit can be provided that can accurately measure a voltage of aninternal circuit without taking much time.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices, shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A testing integrated circuit for a semiconductorchip having an integrated circuit, comprising:a selector, provided inthe integrated circuit of the semiconductor chip, for selecting one of afirst set of signals supplied from external portions of saidsemiconductor chip and a second set of signals used for measuringvoltages at respective predetermined portions in an internal circuit ofsaid semiconductor chip, the first set of signals being converted fromanalog to digital signals during a normal operation of the semiconductorchip; an analog-to-digital converter provided in the integrated circuit,the analog-to-digital converter receiving an analog signal output fromthe selector and producing a digital signal; and a plurality of outputpads disposed in the semiconductor chip, the output pads transmittingthe digital signal from the analog-to-digital converter to the externalportions, the output pads corresponding to a bit quantity of theanalog-to-digital converter.
 2. The testing integrated circuit accordingto claim 1, wherein the selector normally inputs each signal of thefirst set of signals to the analog-to-digital converter.
 3. The testingintegrated circuit according to claim 1, wherein the selector iscontrolled by at least one signal from the second set of signalsgenerated in the internal circuit of said semiconductor chip.
 4. Thetesting integrated circuit according to claim 1, wherein said selectoris controlled by at least one signal from the first set of signals fromthe external portions of the semiconductor chip.
 5. A testing integratedcircuit for a semiconductor chip including an integrated circuit havingan analog-to-digital converter, comprising:a signal input pad disposedon a surface of the semiconductor chip for applying an external signalto the analog-to-digital converter during a normal operation; anamplifier disposed on the semiconductor chip for applying a test modesignal to measure voltage at a predetermined portion in thesemiconductor chip; a selector for selecting one of the external signaland the test mode signal, the external signal corresponding to a signalfor the normal operation of the semiconductor chip and the test modesignal corresponding to a signal for testing the semiconductor chip, theselector transmitting the selected signal to the analog-to-digitalconverter; and a plurality of output pads disposed in the semiconductorchip, the output pads transmitting outputs of the analog-to-digitalconverter to external portions of the semiconductor chip, a quantity ofthe output pads corresponding to a bit quantity of the analog-to-digitalconverter.
 6. The testing integrated circuit according to claim 5,wherein the selector is controlled by an internal signal of thesemiconductor chip.
 7. The testing integrated circuit according to claim5, wherein the selector is controlled by an external signal of thesemiconductor chip.